How about an option to close the thread free of charge, with the ability to have a message as to why its closed, then? It would have to be mediated to make sure people aren't abusing it to bump their messages, or post an update to their sale...

Why not just have a button for the thread poster that puts a big sold across the original post.Looks like a stamp could have a paid in full stamp to ! I have no Idea if its even possible I doubt if its worth Jons time ,but it would be neat.